We shall continue studies on the pathogenesis of Creutzfeldt-Jakob disease in guinea pigs, and enlarge the scope of the investigations to our recent experimental transmissions to hamsters and mice. The strain or strains of the Creutzfeldt-Jakob agent in these different hosts will be approached utilizing various techniques (animal inoculation, physical characteristics of the strain(s), tissue culture studies). The study of experimental Creutzfeldt-Jakob disease in mice of different genotype will facilitate this analysis.